1. Field of the Invention
This invention relates to push button electrical switches and in particularly to an improved, sealed, dual action, tactile feedback, switch assembly having three states or functions.
2. Description of Related Art
It is a constant requirement that switches be made more compact, requiring a minimum of space in an apparatus and yet be simple and reliable. It is another requirement that the switches be sealed in order to be applicable for installation on boards where fluid techniques such wave soldering are used. If the switch is not sealed, internal corrosion of the contacts due to contaminants would occur in the switch.
In addition, for certain applications, the operator expects to feel a switching action such as when going from one switch function to another. In the case of switches having internal contacts implemented with convex discs or domes positioned one above the other in a spaced relationship having their respective centers substantially in alignment. A flex or snap-action occurs when an operator pushes down on a push button which applies a force to the center of the domes. The operator can sense the snapping movement of the center portion of a first dome and then the snapping movement of the center portion of a second dome positioned under the first dome. This sensation is commonly known as "tactile feedback". The flexing of the dome causes an electrical connection to occur first between the upper dome and the lower dome, and then with further pressure on the push button, the lower dome makes electrical connection with a terminal in the base of the switch assembly. Thus, such a switch has a normally open position and two other positions for making electrical connection. Such a switch assembly has to be assembled with low cost parts and low cost efficient means in order to be viable in the market place. Securing the lower dome may provide wider applicability of the switch.
U.S. Pat. No. 4,029,916 issued Jun. 14, 1977 to Pak-Jong Chu discloses a multi-contact push-button switch which has a spring contact plate and a circuit board in superposed position. The spring contact plate has one or more switched positions, each switch position comprising a prestressed domed portion surrounded by a flat short portion. Spring contacts extend radially from the central portion, each contact between a pair of webs. A push button acts on the central portion and pressure on the push button causes the central portion to snap through the plane of the flat sheet portion, with the spring contacts contacting contact areas on the circuit board. However, the switch configuration requires larger packaging and the snap action of one dome provides poorer tactile feed than two dome switches.
U.S. Pat. No. 4,659,881 issued Apr. 21, 1987 to David R. Dowe discloses a multidome switch assembly comprising a pair of conducting resilient domes which snap inwardly to produce corresponding switching functions when downward pressure is applied at the respective centers, and snap outwardly to produce opposite switching functions when the applied pressure is removed. Successive snapping action of the two domes produce corresponding switching functions to provide respective stages of tactile feedback through the push button to the operator. However, securing the lower dome is often a problem to prevent contact with the upper dome especially if the switch is turned upside down. Also, the switch is not a sealed switch which limits its method of connection to a component board.
U.S. Pat. No. 5,564,560 issued Oct. 15, 1996 to Jeffrey D. Minelli et al discloses a dual function button 10 for keyboards and keypads. The button includes a first contact switch which is activated by a first manual pressure. The first control switch is preferably formed by a resilient cover having a conductive pellet on its interim face, and a flexible substrate having spaced contacts below the pellet. The first manual pressure causes the pellet to impinge upon the spaced contacts below the pellets. The first manual pressure causes the pellet to impinge upon the spaced contacts completing a first circuit. The button includes a second contact switch which is activated by a second, greater, manual pressure. The second contact switch includes the resilient cover of the first contact switch, a rigid substrate mounting spaced contacts and a flexible conductive dome mounted on the rigid substrate below the resilient cover. The second manual pressure causes the dome to resiliently deform and impinge upon the contacts closing the second switch. However, this switch is not a discrete component switch and the means for retention of the conductive dome is not clear.